static_dispatch_registration_example

public static class CommandHandlerRegistration
{
    public static void Init()
    {
        // manual registration
        Register<AddProductModel, int>((c, r) => ProductsCommandHandlers.AddProductModel(c, r.Resolve<DbContext>()));
        Register<AddProductReview>((c, r) => ProductsCommandHandlers.AddProductReview(c, r.Resolve<CommandContext>()));
        Register<SetProductModelName>((c, r) => ProductsCommandHandlers.SetProductModelName(c, r.Resolve<CommandContext>()));
    }

    private static void Register<TCommand>(Action<TCommand, IObjectResolver> handler)
        where TCommand : IAPICommand<VoidResult>
    {
        Register<TCommand, VoidResult>((c, r) =>
        {
            handler(c, r);
            return VoidResult.Value;
        });
    }

    private static void Register<TCommand, TResult>(Func<TCommand, IObjectResolver, TResult> handler)
        where TCommand : IAPICommand<TResult>
    {
        ParameterExpression lambdaTargetParameter = Expression.Parameter(typeof(object), "target");

        ParameterExpression commandParameter = Expression.Parameter(typeof(object), "command");
        ParameterExpression objectResolver = Expression.Parameter(typeof(IObjectResolver), "objectResolver");

        UnaryExpression lambdaTargetParameterCast = Expression.Convert(lambdaTargetParameter, handler.Target.GetType());
        UnaryExpression commandParameterCast = Expression.Convert(commandParameter, typeof(TCommand));
        MethodCallExpression methodCall = methodCall = Expression.Call(lambdaTargetParameterCast, handler.Method, commandParameterCast, objectResolver);
        UnaryExpression castMethodCall = Expression.Convert(methodCall, typeof(object));

        var lambda = Expression.Lambda<Func<object, object, IObjectResolver, object>>(castMethodCall, lambdaTargetParameter, commandParameter, objectResolver);
        var compiled = lambda.Compile();

        commandHandlers[typeof(TCommand)] = new Func<object, IObjectResolver, object>((c, r) => compiled(handler.Target, c, r));
    }

    private static readonly Dictionary<Type, Func<object, IObjectResolver, object>> commandHandlers = new Dictionary<Type, Func<object, IObjectResolver, object>>();

    public static IReadOnlyDictionary<Type, Func<object, IObjectResolver, object>> CommandHandlers
    {
        get { return commandHandlers; }
    }
}